The present invention relates to an ink for use in an ink-jet recording, and particularly an ink for use in an ink-jet printer in which ink droplets are discharged from a record head to obtain an ink image on a recording medium.
Conventionally, dyes have been used as the inks for use in the ink-jet recording when forming a recorded image by discharging ink droplets onto a recording medium. The dyes are used to improve the discharge stability and ink preservation stability. However, it is preferable to use pigments rather than inks in view of the water resistance and weather resistance of the recorded objects.
Accordingly, Japanese Patent Laid-Open No. 2-255875 and Japanese Patent Laid-Open No. 4-18462 report an ink having water resistance and weather resistance properties and solves the problem of blurring of characters and the like which have been the controversial points of the conventional dye-based inks, wherein the ink comprises water, a pigment, and a resin emulsion. Such an ink composed of a pigment and a resin emulsion is excellent in the light resistance, water resistance, abrasion resistance, and the like of the printed image.
However, since there are contained in the ink a number of components such as emulsion, in addition to the coloring component or pigment, the bubble forming property of the ink is increased and the discharge property of the ink is degraded. Consequently, the air bubbles are generated in the ink-jet head, and the discharge energy of the ink-jet head is decreased, so that sufficient ink discharge cannot be obtained, leading to the curved flight of the ink dot, poor discharge and the like. Thus, poor images are generated.
As described above, the generation of bubbles leads to the above-mentioned adverse effects on the inkjet head. Then, inks free from generation of bubbles are desirable, but it is impossible to completely suppress the bubble generation because a plurality of materials are mixed together in producing an ink.
Japanese Patent Laid-Open No. 61-250076 discloses an attempt to overcome such problems by regulating the bubble forming property of the surfactant used in an ink. It is certainly conceivable that the bubble forming property of the surfactant in the ink somewhat affects the bubble forming property of the ink. However, the bubble forming property of the ink itself cannot be completely regulated by the bubble forming property of the surfactant. In particular, in an ink which contains, as in the present invention, a plurality of components such as a resin emulsion in addition to a coloring component of pigment, each respective component significantly affects the bubble forming property of the ink.
Furthermore, Japanese Patent Laid-Open No. 9-279068 discloses an attempt of regulating the height of the bubble at the elapsed time of 5 minutes on the basis of the JISK standard concerned. However, it is preferable in an ink-jet system that the bubble generation is suppressed as much as possible, or the bubbles once generated are instantly eliminated.
The present invention intends to solve the problems found in the prior art, and takes as its object the provision of the ink for use in the ink-jet recording which is excellent in the water resistance and lightfast properties, and is additionally stable in the discharge property.
As a result of diligent study intended to overcome the above described problems, the present inventors have come to achieve the present invention by discovering that the purposed ink can be obtained in the following manner: the ink contains at least a solvent containing water as the main component, a solid content containing a coloring material, and at least one type of nonionic surfactant; and the number x of the polyethylene oxide groups and the number y of the polypropylene oxide groups added to the nonionic surfactant are made to fall within the prescribed ranges.
More specifically, the present invention is an ink for use in the ink-jet recording which contains a dye and/or a pigment and water as the indispensable components and a water-insoluble solid content of 1% or more of the whole quantity, wherein the ink comprises:
a nonionic surfactant containing polyethylene oxide groups and polypropylene oxide groups, which is a substance having the structure shown by the following structural formula (1); and the number x of the added ethylene oxide groups and the number y of the added polypropylene oxide groups satisfy the relation that
0 less than xxe2x89xa610,
and the relation that
x/2xe2x88x921 less than y less than x/3+2, 
where q and r are respectively the numbers of the methylene groups, and satisfy the relation that
9xe2x89xa6q+rxe2x89xa611.
And the present invention is an ink for use in an ink-jet recording, wherein the content of the above described nonionic surfactant is no less than 0.001 wt % and no more than 2 wt %.
And the present invention is an ink for use in an ink-jet recording in which the solid content containing a coloring material is composed of a pigment and a water-soluble resin and/or an emulsion and/or a latex.
Thus, the performance of the printed object, particularly the water resistance and abrasion resistance, are improved.
Furthermore, the present invention is an ink for use in the ink-jet recording in which the above described pigment is a self-dispersion pigment.
Additionally, the present invention is an ink for use in the ink-jet recording, further comprising a water-soluble organic solvent in a content of 30 wt % or more.
Thus, the clogging is further prevented and the solubility of the additives is improved.
And the present invention is an ink for use in an ink-jet recording in which the above described water-soluble organic solvent contains 3 wt % or more of an ethyleneglycol based ether.
Furthermore, the present invention is an ink for use in an ink-jet recording in which the above described ethyleneglycol based ether is a triethyleneglycol based ether and/or a tetraethyleneglycol based ether.
Thus, the image density is increased and the image quality is improved.
Additionally, the present invention is an ink for use in an ink-jet recording in which the static surface tension is 25 dyne/m to 50 dyne/m.
Further, the present invention is an ink for use in an ink-jet recording in which the viscosity is 1 cp to 10 cp.